1. Field of the Invention
The present invention relates to a charging device which can be employed in a copying machine, a printer, a facsimile machine or a complex machine including a combination of at least two of them, and also relates to an image forming apparatus employing such a charging device.
2. Description of the Related Art
In an image forming apparatus such as a copying machine or a printer, a surface of an electrostatic latent image carrier is uniformly charged prior to image exposure which is performed for forming an electrostatic latent image on the image carrier. A transfer voltage is applied to a record member such as a paper sheet or an intermediate transfer member for a transfer operation. More specifically, the transfer operation are performed for transferring a toner image formed on the image carrier onto a record member such as a paper sheet. In a multi-color image forming apparatus and others, the transfer operation is also performed for transferring a toner image onto the intermediate transfer member prior to transfer onto the record member. The foregoing transfer voltage is applied onto a rear surface of the record member or the intermediate transfer member for the above transfer operations. Further, a voltage for discharging may be applied for removing electric charges remaining on the electrostatic latent image carrier in a discharging section after the transfer of the toner image.
The foregoing charging and voltage application are performed by various kinds of charging devices. In one of the devices already proposed, a charging member for charging a charge target member, i.e., member to be charged has a sheet-like form.
In a device disclosed, e.g., in Japanese Patent Publication No. 6-90568 (90568/1994), a solid electrode plate is formed of an electric resistance member in a plate form having a volume resistivity of 10.sup.6 10.sup.13 .OMEGA..multidot.cm and a surface resistivity of 10.sup.6 .OMEGA./.quadrature. (10.sup.6 ohm/.quadrature.) or more. A voltage application electrode is adhered onto a first surface of this solid electrode plate, and a second surface of the solid electrode plate is opposed to the charge target member with a minute space of 500 .mu.m or less therebetween, i.e., without establishing a direct contact between them. A voltage is applied to the voltage application electrode for charging.
According to the charging device taught by Japanese Patent Publication No. 6-90568, however, it is difficult to prevent contact between the solid electrode plate and the charge target member and to keep a constant space between them, so that abnormal discharging is liable to occur at an end of the solid electrode plate, resulting in defective charging such as irregular charging.